Tunable templating layers for perpendicularly magnetized heusler films

ABSTRACT

A device including a templating structure and a magnetic layer on the templating structure is described. The templating structure includes D and E. A ratio of D to E is represented by D 1-x E x , with x being at least 0.4 and not more than 0.6. E includes a main constituent. The main constituent includes at least one of Al, Ga, and Ge. Further, E includes at least fifty atomic percent of the main constituent. D includes at least one constituent that includes Ir, D includes at least 50 atomic percent of the at least one constituent. The templating structure is nonmagnetic at room temperature. The magnetic layer includes at least one of a Heusler compound and an L1 0  compound, the magnetic layer being in contact with the templating structure.

BACKGROUND OF THE INVENTION

Heusler compounds are a class of materials having the representativeformula X₂YZ, where X and Y are transition metals or lanthanides, and Zis from a main group element. Due to the chemical distinction between X(or Y) and Z, they form a unique structure defined by the space groupsymmetry L2₁ (or D0₂₂ when they are tetragonally distorted), where fourface-centered cubic structures penetrate each other. The properties ofHeusler compounds are strongly dependent on the atomic ordering of theelements constituting the compounds. Thus, the fabrication of highquality Heusler films typically requires high temperature thermalprocesses: for example, deposition at temperatures significantly aboveroom temperature and/or thermal annealing at high temperatures (200° C.or higher). Such high deposition temperatures may adversely affect theproperties of other portions of the device in which the Heusler compoundis desired to be used. However, Heusler compounds and L1₀ compounds havestill attracted interest as candidate materials for various spintronicapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 illustrates an embodiment of the templating concept. A and Xrepresent transition metal elements, and E and Z represent main groupelements.

FIG. 2 illustrates an embodiment of the synthetic antiferromagnetic(SAF) structure with a Heusler bilayer separated by an IrAl spacerlayer. X and X′ represent transition metal elements, and Z and Z′represent main group elements.

FIG. 3 shows XRD scans of 300 Å thick Ir_(1-x)Al_(x) films on aMgO/MgO(001) substrate. IrAl films were deposited at room temperatureand annealed in situ at various temperatures in vacuum.

FIG. 4 shows a high resolution TEM image of 20 Å thick Mn₃Sn film on anIrAl templating layer that was grown on a MgO(001) single crystalsubstrate (not shown).

FIG. 5 shows root mean square (RMS) roughness (r_(rms)) versus annealingtemperature of an IrAl templating layer.

FIG. 6 presents room temperature perpendicular magneto-optical Kerreffect (P-MOKE) hysteresis loops of 20 Å thick Mn₃Sn films on a 300 ÅIrAl templating layer. The IrAl layer was deposited at varioustarget-to-substrate distances with 135 mm being the typical value.

FIG. 7 shows a perpendicular MOKE hysteresis loop from an IrAltemplating layer grown on a MgO(001) single crystalline substrate atroom temperature.

FIG. 8 illustrates part of a device that incorporates the templating andHeusler layers described herein.

FIG. 9 illustrates an embodiment of a magnetic tunnel junction devicethat incorporates the templating and Heusler layers described herein.

FIG. 10 shows the c-axis lattice spacing as a function of IrAl and CoAltemplating layer thicknesses.

FIG. 11 indicates the in-plane lattice constant for differentthicknesses of embodiments of IrAl and CoAl/IrAl bilayers.

FIG. 12 shows P-MOKE hysteresis loops of a 30 Å thick Mn₃Ge Heuslerlayer on a CoAl/IrAl templating bilayer that was grown on a MgO(001)single crystalline substrate.

FIG. 13 shows P-MOKE hysteresis loops of a 20 Å thick Mn₃Sn Heuslerlayer on the templating layers IrAl, CoAl/IrAl, and CoAl, grown on aMgO(001) single crystalline substrate.

FIG. 14 illustrates layers formed when employing one method herein(including two different multilayered structures), in which a targetin-plane lattice constant is selected prior to the deposition of thelayers.

FIG. 15 illustrates part of a device that incorporates multilayered andHeusler layers described herein.

FIG. 16 illustrates an embodiment of a device that incorporates atemplating structure and a Heusler layer, which can be used as a memoryelement in a racetrack device.

FIG. 17 illustrates an embodiment of a magnetic tunnel junction devicethat incorporates a templating structure and a Heusler layer, asdescribed herein.

FIG. 18 illustrates an embodiment of a magnetic tunnel junction devicethat incorporates a templating structure and a Heusler layer that actsas a pinning layer.

FIG. 19 shows a P-MOKE hysteresis loop from the illustrated Heuslerstack, which includes an 11 Å IrAl spacer layer. The magnetic moments ofthe two Heusler-containing layers at different positions in thehysteresis loop are indicated with thick arrows, whereas the thin arrowsindicate the scan direction. (The illustrated Heusler stack on theleft-hand side shows magnetic moments corresponding to the case nearzero field—compare with the loop shown on the right-hand side.)

FIG. 20 shows P-MOKE hysteresis loops of embodiments of Heusler stacks(e.g. left hand side of FIG. 20) having different IrAl spacer layers ofthicknesses 7, 9, and 11 Å.

FIG. 21 P-MOKE hysteresis loops of embodiments of Heusler stacks (e.g.left hand side of FIG. 21) having different CoAl spacer layerthicknesses, up to 16 Å.

FIG. 22 illustrates an embodiment of a synthetic antiferromagnetic (SAF)structure that incorporates the templating and Heusler layers describedherein, in which the magnetic moments of the Heusler layers areperpendicular to a multilayered structure that separates the Heuslerlayers.

FIG. 23 illustrates an embodiment of a SAF that incorporates thetemplating and Heusler layers described herein, in which the magneticmoments of the Heusler layers are parallel to a multilayered structurethat separates the Heusler layers.

FIG. 24 illustrates an embodiment of a magnetic tunnel junction devicethat incorporates the templating and Heusler layers described herein,thereby forming a memory element that includes an SAF.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

New magnetic materials are needed to allow for scaling of magneticdevices such as spin transfer torque magnetic random access memories(STT MRAM beyond the 20 nm node. These materials are desired to havevery large perpendicular magnetic anisotropy (PMA) and, for integrationpurposes, be compatible with conventional CMOS technologies. Suchmagnetic materials form electrodes of magnetic tunnel junction (MTJ)based memory elements. A mechanism for switching the state of the MTJelement is using spin polarized tunneling currents that are passedthrough the MTJ. The magnitude of this current is limited by the size ofthe transistors used to provide the write current. This means that thethickness of the electrode must be sufficiently small that it can beswitched by the available current. For magnetization values of ˜1000emu/cm³, the electrode should have a thickness that does not exceedapproximately 1 nm. Recently it has been shown that using templatinglayers, such as CoAl, CoGa, CoSn, or CoGe, it is possible to deposit anultrathin Heusler layer (thickness of ˜1 nm) having bulk-like magneticproperties. These ultrathin Heusler compound films of even a single unitcell thickness showed perpendicular magnetic anisotropy and squaremagnetic hysteresis loops, making them candidate materials for use inSTT-MRAM and racetrack memory applications.

Moreover, the ultrathin Heusler compound films deposited on templatinglayers, such as CoAl, CoGa, CoSn, or CoGe, grow epitaxially, i.e., theultrathin Heusler compound has the same or substantially same in-planelattice constant as that of the templating layer. There exists asignificant lattice mismatch between these templating layers and the MgOtunnel barrier (>5%), which may result in low tunnel magnetoresistance(TMR), as a result of incoherent tunneling through the tunnel barrier.Such a reduction in TMR is undesirable for device performance.

As mentioned above, the ultrathin Heusler compound films withperpendicular magnetic anisotropy and square magnetic hysteresis loopsmay be used in STT-MRAM and racetrack memory applications. In suchapplications, a synthetic anti-ferromagnet (SAF) may be used. In anSTT-MRAM application, the reference layer can include an SAF structurebecause this structure has very small fringing fields, which are theprimary cause of the offset fields observed in the measured hysteresisloops of the storage layer. In a racetrack memory, the domain wallvelocities in nanowires of an SAF structure are significantly higherthan those in the nanowires of conventional ferromagnets. The SAFstructures formed from conventional ferromagnets use Ru as thenon-magnetic spacer layer. The family of tetragonal Heusler compounds,which include Mn₃Z with Z=Ge, Sn, and Sb, have a layered structure ofalternating layers of Mn—Mn and Mn—Z. The use of a known elementalspacer layer (e.g., Ru alone) does not work for structures that includetwo Heusler layers, since elemental Ru is unable to replicate theordering of a Heusler layer underneath it; thus, it is unable to promotethe ordering in a Heusler layer grown over the Ru spacer layer.

The exemplary embodiments are described in the context of particularmethods, magnetic junctions and magnetic memories having certaincomponents. One of ordinary skill in the art will readily recognize thatthe present invention is consistent with the use of magnetic junctionsand magnetic memories having other and/or additional components and/orother features not inconsistent with the present invention. The methodand system are also described in the context of current understanding ofthe spin transfer phenomenon, of magnetic anisotropy, and other physicalphenomenon. Consequently, one of ordinary skill in the art will readilyrecognize that theoretical explanations of the behavior of the methodand system are made based upon this current understanding of spintransfer, magnetic anisotropy and other physical phenomena. However, themethod and system described herein are not dependent upon a particularphysical explanation. One of ordinary skill in the art will also readilyrecognize that the method and system are described in the context of astructure having a particular relationship to the substrate. One ofordinary skill in the art will readily recognize that the method andsystem are consistent with other structures. In addition, the method andsystem are described in the context of certain layers being syntheticand/or simple. However, one of ordinary skill in the art will readilyrecognize that the layers could have another structure. Furthermore, themethod and system are described in the context of magnetic junctionsand/or substructures having particular layers. One of ordinary skill inthe art will readily recognize that magnetic junctions and/orsubstructures having additional and/or different layers not inconsistentwith the method and system could also be used. Moreover, certaincomponents are described as being magnetic, ferromagnetic, andferrimagnetic. As used herein, the term magnetic could includeferromagnetic, ferrimagnetic or like structures. Thus, as used herein,the term “magnetic” or “ferromagnetic” includes, but is not limited toferromagnets and ferrimagnets. As used herein, “in-plane” issubstantially within or parallel to the plane of one or more of thelayers of a magnetic junction. Conversely, “perpendicular” and“perpendicular-to-plane” corresponds to a direction that issubstantially perpendicular to one or more of the layers of the magneticjunction. The method and system are also described in the context ofcertain alloys. Unless otherwise specified, if specific concentrationsof the alloy are not mentioned, any stoichiometry not inconsistent withthe method and system may be used.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. It is noted that the use of anyand all examples, or exemplary terms provided herein is intended merelyto better illuminate the invention and is not a limitation on the scopeof the invention unless otherwise specified. Further, unless definedotherwise, all terms defined in generally used dictionaries may not beoverly interpreted.

A device including a templating structure and a magnetic layer on thetemplating structure is described. The templating structure includes Dand E. A ratio of D to E is represented by D_(1-x)E_(x), with x being atleast 0.4 and not more than 0.6. E includes a main constituent. The mainconstituent includes at least one of Al, Ga, and Ge. Further, E includesat least fifty atomic percent of the main constituent. D includes atleast one constituent that includes Ir, D includes at least 50 atomicpercent of the at least one constituent. The templating structure isnonmagnetic at room temperature. The magnetic layer includes at leastone of a Heusler compound and an L1₀ compound, the magnetic layer beingin contact with the templating structure. In some embodiments, thetemplating structure includes alternating layers of D and E. In someembodiments, x is at least 0.47 and not more than 0.54. In some suchembodiments, the templating structure has a thickness of at least thirtyAngstroms and not more than six hundred Angstroms such that thetemplating structure has a lattice constant (e.g. an in-plane latticeconstant) of at least 2.8 Angstroms and not more than 3.05 Angstroms. Insome embodiments, the templating structure has a thickness of not morethan five hundred and fifty Angstroms. In some such embodiments, thethickness of the templating structure is not more than five hundred andten Angstroms. In some embodiments, the templating structure has athickness of not more than five hundred Angstroms. In some embodiments,the magnetic layer has a thickness of not more than five nanometers. Themagnetic layer may be not more than three nanometers thick. In some suchembodiments, wherein the magnetic layer has a thickness of not more thanone unit cell. In some embodiments, the magnetic layer includes at leastone of Mn_(3.1-y)Ge, Mn_(3.1-y)Sn, Mn_(3.1-y)Sb, Mn_(3.1-s)Co_(1.1-t)Sn,a MnGa alloy, a MnAl alloy, an FeAl alloy, a MnGe alloy, a MnSb alloy,and a MnSn alloy, with y being at least 0 and not more than 1.1, andwith s being greater than zero and not more than 1.2 and t is greaterthan zero and not more than 1.0. The magnetic layer may be magneticas-deposited and/or may be deposited at room temperature. In someembodiments, the device an additional magnetic layer and a tunnelingbarrier layer between the additional magnetic layer the magnetic layer.

A method for providing a device is also described. The method includesproviding a templating structure and providing a magnetic layer on thetemplating structure. The templating structure includes D and E. Theratio of D to E is represented by D_(1-x)E_(x), with x being at least0.4 and not more than 0.6. In some embodiments, x is at least 0.47 andnot more than 0.54. E includes a main constituent, which is at least oneof Al, Ga, and Ge. E includes at least fifty atomic percent of the mainconstituent. D includes at least one constituent that includes Ir. Dincludes at least 50 atomic percent of the constituent(s). Thetemplating structure may be nonmagnetic at room temperature. Themagnetic layer includes at least one of a Heusler compound and an L1₀compound and may be in contact with the templating structure.

In some embodiments, providing the templating structure includesdepositing alternating layers of D and E. The templating structure maybe annealed at an anneal temperature of at least two hundred degreesCelsius. In some embodiments, the anneal temperature is at least fourhundred degrees Celsius. In some embodiments, a target lattice constantof the magnetic layer is selected. In such embodiments, providing thetemplating structure further includes depositing the templatingstructure to a thickness of at least thirty Angstroms and not more thansix hundred Angstroms such that the templating structure has a latticeconstant (e.g. an in-plane lattice constant) of at least 2.8 Angstromsand not more than 3.05 Angstroms. In some embodiments, the templatingstructure has a thickness of not more than five hundred and fiftyAngstroms. In some such embodiments, the thickness of the templatingstructure is not more than five hundred and ten Angstroms. In someembodiments, the templating structure has a thickness of not more thanfive hundred Angstroms. The lattice constant may be chosen to correspondto the target lattice constant. The magnetic layer has a thickness ofnot more than five nanometers in some embodiments. For example, themagnetic layer may have a thickness of not more than one unit cell. Insome embodiments, the magnetic layer includes at least one ofMn_(3.1-y)Ge, Mn_(3.1-y)Sn, Mn_(3.1-y)Sb, and Mn_(3.1-s)Co_(1.1-t)Snwith y being at least 0 and not more than 1.1, and with s being greaterthan zero and not more than 1.2 and t is greater than zero and not morethan 1.0. In some embodiments, the method further includes providing anadditional magnetic layer and providing a tunneling barrier layerbetween the additional magnetic layer and the magnetic layer. In someembodiments, providing the magnetic layer further includes depositingthe magnetic layer at room temperature.

IrAl templating layer(s) which promote growth of ultrathin Heuslercompound films with perpendicular magnetic anisotropy and squaremagnetic hysteresis loops are described. Disclosed herein is atemplating layer whose in-plane lattice constant can be pre-selectedover a significant range that includes the lattice constant of the MgOtunnel barrier. Disclosed herein is a spacer layer that promotes theformation of an SAF structure between Heusler layers. It is shown hereinthat an IrAl alloy spacer layer having the CsCl structure inducesanti-ferromagnetic coupling between two tetragonal Heusler compoundlayers separated by that spacer layer.

Disclosed herein are highly textured, very smooth, high qualityultrathin films of Heusler compounds, which can be fabricated without athermal annealing process (or with a lower temperature thermal annealingprocess), using a non-magnetic templating layer. The templating layermay be formed from a binary alloy of Ir—Al with the B2 structure, thecubic version of L1₀. The templating layer can be deposited at roomtemperature and is atomically ordered (i.e., alternating atomic layersof Ir and Al are formed), even in the as-deposited state. Ultrathinfilms of Heusler compounds deposited on these templating layers arehighly epitaxial, atomically ordered, high quality films with excellentmagnetic properties, including especially high values of perpendicularmagnetic anisotropy and square magnetic hysteresis loops (with theremanent moment in zero magnetic field being close to the saturationmoment). This is attributed to the similarity between the B2 symmetry ofthe templating layer and the L2₁ or D0₂₂ symmetry of the Heusler layer.

A characteristic of the underlayer (e.g. a templating layer) is that itis composed of elements that are similar to those of the Heuslercompound. For example, any intermixing or diffusion of the Al from theIrAl underlayers into the Heusler layer does not significantly changethe properties of the Heusler layer, since Al is from the class of Zelements from which the Heuslers are formed. Similarly, underlayers thatpartially replace Al with other Z elements, such as Ga, Ge and/or Sn,are suitable for the underlayers. The Ir within the IrAl underlayers canalso diffuse into the Heusler without causing significant degradation ofthe magnetic properties of the Heusler layer. Thus, the underlayers areadvantageously formed from A-E alloys, where A is a transition metal andE is a main group element.

Another property of the underlayer is that it can promote the desiredordering of the Heusler compound. The underlayer will generally haveterraces with atomic steps between neighboring terraces, in which eachof the steps separates a terrace with a surface formed from Ir from aterrace formed from Al. Due to the chemical affinity of X (or Y) to Al,and of Z to Ir, the underlayer promotes the desired ordering of theHeusler compound at modest temperatures even as low as room temperature,as illustrated in FIG. 1. Annealing does not significantly improve themagnetic properties of the Heusler compound.

Such Heusler compounds are used herein to form memory storage elements(e.g., racetrack and MRAM) and synthetic anti-ferromagnets, which aredisclosed herein. Associated methods of formation, including a method ofpreselecting a desired lattice constant of a structure are alsodisclosed.

IrAl Templating Layer

Single crystal epitaxial films of Ir_(1-x)Al_(x) alloy were grown bydc-magnetron sputtering onto MgO buffer layers overlying MgO(001) singlecrystal substrates, in an ultra-high vacuum (UHV) chamber with a basepressure of ˜1×10⁻⁹ Torr. The MgO substrates were cleaned in anultrasonic bath of methanol for 30 min, treated in an isopropyl alcohol(IPA) vapor degreaser for 2 min, dried with N₂ gas at 65° C. for 15 min,and then transferred into the deposition chamber where they wereannealed at 650° C. for 30 min in ultra-high vacuum (UHV). The MgObuffer layer was prepared by depositing 20 Å thick MgO at roomtemperature using rf-magnetron sputtering from a MgO target. For all themagnetron sputtering processes, Argon was the sputtering gas at atypical gas pressure of 3 mTorr. Films of 300 Å thick IrAl weredeposited at room temperature. These films were either not annealed orannealed at various temperatures T_(AN)=200, 300, 400, and 500° C. for30 minutes. The composition of the IrAl layers was determined to beIr_(51.6)Al_(48.4) by Rutherford backscattering (RBS) measurement.Elements other than those discussed herein may be present in thedisclosed structures. For example, although pristine Ir and Al layersare frequently used, these layers may include other elements thatconstitute a significant atomic percentage of these layers (e.g., up to50 atomic percent).

X-ray diffraction (XRD) θ-2θ scans were performed on these films. TheseXRD measurements were performed using a Bruker D8 Discover system atroom temperature. FIG. 3 shows XRD scans of IrAl films annealed atvarious temperatures T_(AN) for 30 minutes. These IrAl films weredeposited from a single IrAl alloy target. The data were compared withthose taken from an IrAl film which was not annealed. The data show themain IrAl (002) peak at 2θ32 ˜57° as well as the IrAl (001) peak at2θ=˜27.5°. The existence of the IrAl (001) superlattice peak clearlyindicates that there is an alternate layering of Ir and Al even in theabsence of annealing; even when annealing is employed, the alternatelayering structure is preserved. The X-ray diffraction associated withthe substrate was observed for all samples and is labeled as theMgO(002) peak.

FIG. 4 is a high resolution, scanning transmission electron microscopy(HR-STEM) image of a typical 20 Å Mn₃Sn layer grown on an IrAltemplating layer. The stack of this sample was MgO(001)/20 Å MgO/300 ÅIrAl/20 Å Mn₃Sn/20 Å MgO/20 Å Ta. The IrAl templating layer consists ofalternating layers of Ir and Al in agreement with the XRD measurementsdetailed in FIG. 3. The epitaxial matching of 20 Å thick Mn₃Sn layerswith the IrAl templating layer is clearly seen. Furthermore, the desiredordering within the Heusler layer is evident: The Mn—Sn layers are alsodistinguishable from the Mn—Mn layers, showing the alternating atomiclayers and even the desired ordering within each Mn—Sn layer.

Atomic force microscopy was performed to probe the surface morphology of300 Å thick IrAl templating layers. FIG. 5 shows the root-mean-squaredsurface roughness (r_(rms)) for various annealing temperatures. Thefilms show a very smooth surface independent of annealing temperature,with r_(rms)˜1 Å.

Mn₃Z Tetragonal Heusler

20 Å-thick Mn₃Sn films were deposited at room temperature by magnetronsputter deposition on an IrAl templating layer. The stacks were cappedby 20 Å thick MgO and 20 Å thick Ta to prevent ambient oxidation of theHeusler layer. The resulting structures were of the form: MgO(001)/20 ÅMgO/300 Å IrAl/20 Å Mn₃Sn/20 Å MgO/20 Å Ta. The IrAl layers weredeposited at room temperature with various substrate-to-targetdistances. The typical substrate-to-target distance is ˜135 mm in thedeposition tool. Four deposition positions were evaluated: 135 mm, 125mm, 120 mm, and 113 mm (i.e., the substrate was also placed closer tothe target than the typical substrate-to-target distances of 135 mm, by10, 15, and 22 mm, respectively). Table 1 (see end of specification)includes the RBS composition of the IrAl layer at these four depositionpositions. As the substrate-to-target distance is decreased, the Ircontent of the film is decreased. FIG. 6 shows the perpendicularmagneto-optical Kerr effect (P-MOKE) hysteresis loops of Mn₃Sn layer fordeposition positions of 135 mm, 125 mm, and 120 mm. Interestingly, themagnetic properties of Mn₃Sn are independent of these depositionpositions, showing excellent PMA for all the films using an IrAltemplating layer. Abrupt switching of the magnetic moment implies thatthere is no second phase. These results clearly demonstrate that an IrAllayer at compositions close to 1:1 promotes ordering within an ultrathinMn₃Sn Heusler compound, even when deposited at room temperature withoutany subsequent annealing, with the Heusler compound showing excellentPMA. FIG. 7 shows the P-MOKE signal from a MgO(001)/20 Å MgO/300 ÅIrAl/20 Å MgO/20 Å Ta sample, which is the sample without the Heuslerlayer. The lack of any magnetic field-dependent MOKE signal clearlyindicates that the IrAl templating layer is non-magnetic at roomtemperature. Though the data discussed above were collected with astructure that includes an IrAl templating layer and a Mn₃Sn Heuslercompound, the IrAl templating layer is equally effective in promotingdesired ordering when used with Mn₃Ge, Mn₃Sb and Mn₃Ga Heuslercompounds. The Heusler compounds can be Mn_(3.1-x)Ge, Mn_(3.1-x)Sn,Mn_(3.1-x)Sb, and Mn_(3.1-x)Ga, with x being in the range from 0 to 1.1.Alternatively, the Heusler compound used may be a ternary Heusler, suchas Mn_(3.1-x)Co_(1.1-y)Sn, wherein x≤1.2 and y≤1.0. Furthermore, theIrAl templating layer is effective in inducing order within L1₀compounds, whose constituent elements include one transition metalelement and a main group element. Possible L1₀ compounds include MnAlalloys, MnGa alloys, MnSn alloys, MnGe alloys, MnSb alloys, and FeAlalloys.

The structural ordering of ultrathin layers is likely due to thediffering chemical properties of the elements Ir and Al in thetemplating layer. As an alternative to Al, Al alloys such as AlSn, AlGe,AlGaGe, AlGaSn, AlGeSn, and AlGaGeSn may be employed. Furthermore, usingan Ir—Co alloy instead of just Ir within the IrAl templating layer (withthe Ir—Co alloy having the composition Ir_(x)Co_(1-x), with x being inthe range 0.0001 to 0.9999) will also promote structural ordering ofultrathin Heusler layers. Binary (X=Y) and ternary Heusler alloysconsist of two or three different types of atoms, respectively. In X₂YZHeuslers, the Z main group element typically has a high chemicalaffinity for X and Y. In this context, the formation of an orderedstructure should take place, irrespective of the choice of Z.

The structure described above can be used in racetrack memory devices.For example, the racetrack may be a nanowire that may include asubstrate, an optional seed layer, a templating layer, and a firstmagnetic layer of a Heusler compound (see FIG. 8). (The electrode on theleft side of the structure is part of the electrical circuit used topass flow current through the device—see also FIGS. 9, 14-18, and 22-24.The electrodes called out in the various stacks herein representmagnetic layers.) Magnetic domain walls may be moved along thisracetrack, as described in U.S. Pat. No. 6,834,005. Data may be read outof (and stored in) the racetrack by interrogating (or changing) theorientation of the magnetic moment of the magnetic material betweenadjacent domain walls within the racetrack.

FIG. 8 illustrates a device that includes an optional seed layeroverlying a substrate. The top two layers form a device that includes amagnetic (e.g. Heusler) layer that overlies a templating layer(multi-layered structure) of the sort described herein. Thismulti-layered structure is non-magnetic at room temperature and includesalternating layers of D and E, which are now defined. (The multi-layeredstructure of FIG. 8 is shown in greater detail in FIG. 1, where D isrepresented by the letter A.) E comprises at least one of (e.g. one, twoor more of) Al, Ga, and Ge, with the composition of the structure beingrepresented by D_(1-x)E_(x), in which x is in the range from 0.47 to0.54 in some embodiments (e.g. at least 0.4 and not more than 0.6 insome embodiments), and with this main group element representing atleast 50 atomic percent of E. On the other hand, D comprises at leastone element that includes Ir, with Ir representing at least 50 atomicpercent of D. (D may optionally include up to at least 10 percent ormore of Co.) The magnetic layer may advantageously be a pure Heuslercompound; alternatively, it may include a Heusler and/or an L1₀ compound(e.g., a compound selected from the group consisting of MnGa, MnAl,FeAl, MnGe, MnSb, and MnSn alloys). This magnetic layer (which may beless than 5 nm thick; data obtained with a thickness of just one unitcell show satisfactory magnetism) may contact and overlie themulti-layered structure, as shown in FIG. 8. Other thicknesses andcompositions are possible.

In some embodiments, the Heusler compound of FIG. 8 may be selected fromthe group consisting of Mn_(3.1-x)Ge, Mn_(3.1-x)Sn, and Mn_(3.1-x)Sb,with x being in the range from 0 to not more than 1.1. Alternatively,the Heusler compound may be a ternary Heusler, e.g.,Mn_(3.1-x)Co_(1.1-y)Sn, in which x≤1.2 and y≤1.0. The Heusler may alsoadvantageously include Co.

Standard deposition techniques may be used to form the devices of FIG. 8and FIG. 9 (discussed below). By way of example, Ir and Al may bedeposited onto a substrate, thereby forming a composite layer on it. Thecomposite layer may then be annealed (at a temperature of at least 200°C. and at least 400° C. in some embodiments), so that at least one layerof Ir and at least one layer of Al are formed from the composite layer,resulting in the formation of the multi-layered structure. Additionallayers, such as a magnetic (Heusler) layer may be formed over themulti-layered structure (e.g., via deposition).

The structure described above in connection with FIG. 8 can also be usedas part of an MRAM memory device, and one such MRAM memory element isshown in FIG. 9. As with MRAM elements generally, a tunnel barrier issituated between two magnetic electrodes, one of which has a fixedmagnetic moment and the other of which has a magnetic moment that isswitchable, thereby permitting the recording and erasing of data. TheHeusler layer, which may be either ferro- or ferri-magnetic, overlies atemplating layer which in turn overlies a substrate; the Heusler layerhas its magnetic moment aligned perpendicular to the layer plane. Anoptional seed layer may be interposed between the substrate and thetemplating layer. An optional polarization enhancement layer may be usedto increase performance and may include Fe, a CoFe alloy, and/orCo₂MnSi. The tunnel barrier may be MgO (001), although other(001)-oriented tunnel barriers may be used, such as CaO and LiF. In someembodiments, MgAl₂O₄ can be used as a tunnel barrier, with its latticespacing being selected by controlling the Mg—Al composition, therebyresulting in better lattice matching with the Heusler compounds (e.g.,the composition of this tunnel barrier can be represented asMg_(1-z)Al_(2+(2/3)z)O₄, wherein −0.5<z<0.5). The magnetic electrodeoverlying the tunnel barrier may comprise Fe, a CoFe alloy, or a CoFeBalloy, for example. If the magnetic layer on top of the barrier has afixed magnetic moment, then its moment can be stabilized by placing asynthetic antiferromagnet (SAF) in proximity with it (e.g., above it, asshown). The capping layer may comprise Mo, W, Ta, Ru, or a combinationthereof. Current may be induced by applying a voltage between the twomagnetic electrodes, which are separated by the tunnel barrier.

IrAl Templating Layer with Tunable Lattice Constant

FIG. 10 shows the out-of-plane c-axis lattice spacing of the Ir—Al andCo—Al templating layers. The resulting structures are of the formMgO(001)/20 Å MgO/x Å IrAl/20 Å MgO/20 Å Ta where x=30, 45, 60, 75, 100,200, 300 and 500 Å and MgO(001)/20 Å MgO/y Å CoAl/20 Å MgO/20 Å Ta,where y=50, 100, 150, and 300 Å. The c-axis lattice spacing wasdetermined by X-ray diffraction (XRD) θ-2θ scans. For the embodimentsshown, the c-axis lattice spacing for the CoAl templating layer isindependent of the CoAl thickness studied here, whereas the c-axislattice spacing for the IrAl templating layer varies systematically from3.05 to 3.25 Å, as a function of the IrAl layer thickness. Thisvariation can be extended even further by using a bilayer of CoAl/IrAl.Assuming the validity of the Poisson effect (i.e., unit cell volume isconserved) and using the known value for the volume of the IrAl unitcell, the in-plane lattice constant for IrAl templating layers can beestimated. FIG. 11 is a plot of the calculated in-plane lattice constantfor various thicknesses of IrAl in a single IrAl layer or within anIrAl/CoAl bilayer. (Note that the possibly limiting cases of CoAl onlyand MgO are also included for comparison.) In some embodiments, thein-plane lattice constant can be selected in advance to be anywhere from˜2.83 to ˜3.05 Å (e.g. at least 2.8 Angstroms and not more than 3.1Angstroms in some embodiments). This range includes (overlaps with) thelattice match to the MgO tunnel barrier.

Mn₃Z Heusler Compound

An IrAl templating layer is disclosed that is capable of inducing orderin ultra-thin Mn₃Z (e.g. Mn₃Ge, Mn₃Sn, and Mn₃Sb) Heusler filmsincluding when deposited at room temperature. The stack discussed hereinconsists of MgO(001)/20 Å MgO/100 Å CoAl/300 Å IrAl/30 Å Mn₃Ge/20 ÅMgO/20 Å Ta. Thus, Mn₃Ge is discussed. FIG. 12 shows the P-MOKEhysteresis loops obtained for this structure. A square hysteresis loopindicates substantial remanent magnetization at zero applied field. Thisresult demonstrates that the IrAl templating layer can induce order inan ultrathin Mn₃Ge layer even after deposition of the Heusler compoundat room temperature. Likewise, an IrAl templating layer is effective inpromoting order within Mn₃Sb and Mn₃Ga Heusler compounds. The binaryHeusler compounds may advantageously have a composition given byMn_(3.1-x)Ge, Mn_(3.1-x)Sn, Mn_(3.1-x)Sb, and Mn_(3.1-x)Ga, with x beingin the range from 0 to not more than 1.1. Alternatively, the Heuslercompound may be a ternary Heusler, such as Mn_(3.1-x)Co_(1.1-y)Sn,wherein x≤1.2 and y≤1.0. As for the CoAl templating layer, an IrAltemplating layer may be effective in inducing order within L1₀compounds, whose constituent elements include one transition metalelement and a main group element. Possible L1₀ compounds include MnAlalloys, MnGa alloys, MnSn alloys, MnGe alloys, MnSb alloys, and FeAlalloys.

FIG. 13 includes P-MOKE square hysteresis loops for 20 Å Mn₃Sn Heuslerlayers deposited on IrAl, CoAl/IrAl, and CoAl templating layers. Thisillustrates that the embodiment of Mn₃Sn Heusler layer is PMA even whenits in-plane lattice constant is varied from ˜2.84 to 2.92 Å (e.g. 2.8Angstroms to 2.95 Angstroms in some embodiments).

Based on the results described above, a target in-plane lattice constantcan be achieved with either of the configurations of the templatingstructure shown in FIGS. 14 and 15. A first configuration of thetemplating structure (see FIG. 14) may include Ir and Co-containingmultilayered structures in contact with each other, in either order. Thethicknesses of the Ir and Co-containing multilayered structures arechosen to achieve the target in-plane lattice constant. A secondconfiguration of the templating structure (see FIG. 15) may employvarious thicknesses of the Ir-containing multilayered structure or aCo-containing multilayered structure.

Thus, the technology described herein lends itself to a method offorming a device whose associated lattice constant can be engineered.For example, for a device that includes at least one multi-layeredstructure and a first magnetic layer (e.g. a Heusler and/or an L1₀compound, having at thickness of less than 5 nm) grown over (e.g., incontact with) the multi-layered structure, such a method includesselecting a target lattice constant for the first magnetic layer. If thefirst magnetic layer is a Heusler compound, it may be selected from thegroup consisting of Mn_(3.1-x)Ge, Mn_(3.1-x)Sn, and Mn_(3.1-x)Sb, with xbeing in the range from at least 0 to not more than 1.1. The magneticlayer may be also be advantageously doped with Co. Alternatively, theHeusler compound may be a ternary Heusler of the formMn_(3.1-x)Co_(1.1-y)Sn, wherein x≤1.2 and y≤1.0. If the first magneticlayer is an L1₀ compound, it may be selected from the group consistingof MnGa, MnAl, FeAl, MnGe, MnSb, and MnSn alloys.

A multi-layered Ir-containing structure (that is non-magnetic at roomtemperature) is grown, in which the Ir-containing structure has alattice constant and comprises alternating layers of Ir with E. Thecomposition of the Ir-containing structure is represented byIr_(1-x)E_(x), wherein E comprises at least one other element thatincludes Al, with x being in the range from 0.4 to not more than 0.6(e.g. at least 0.47 to not more than 0.54). The Ir-containing structureis grown such that its lattice constant matches the target latticeconstant, by choosing the number of Ir layers and the number of Allayers in the Ir-containing structure, so that the desired thickness ofthe Ir-containing structure is obtained. In some embodiments, “matching”includes other than exact matches. For example, “matching” may includethe Ir-containing structure's lattice constant being within five percentof the target lattice constant. In some embodiments, “matching” includesthe Ir-containing structure's lattice constant being not more than threepercent different from the target lattice constant. In some suchembodiments, “matching” includes the Ir-containing structure's latticeconstant being not more than one percent different from the targetlattice constant. As indicated in FIG. 11, this thickness (for a givenstructure) determines the associated lattice constant. A magnetic layeris grown over the Ir-containing structure (either in contact with it, orin proximity with it as when an additional multi-layered structure isincorporated into the stack). In some embodiments, the thickness of thestructure is at least twenty Angstroms and not more than six hundredAngstroms. In some such embodiments, thickness may be at least thirtyAngstroms. In some embodiments, the templating structure has a thicknessof not more than five hundred and fifty Angstroms. In some suchembodiments, the thickness of the templating structure is not more thanfive hundred and ten Angstroms. In some embodiments, the templatingstructure has a thickness of not more than five hundred Angstroms.

In some embodiments, prior to growing the Ir-containing structure, amulti-layered Co-containing structure is grown that is non-magnetic atroom temperature, with the Co-containing structure having a latticeconstant and including alternating layers of Co with E′. The compositionof the Co-containing structure is represented by C_(1-y)E′_(y), in whichE′ comprises at least one other element that includes Al, with y beingin the range of 0.4 to not more than 0.6 (e.g. at least 0.47 to not morethan 0.54). In some embodiments, E and/or E′ may be an AlGe alloy.Similarly, in some embodiments, E and/or E′ may be an AlGa alloy.

The Co-containing structure is grown by choosing the number of Co layersand the number of Al layers in the Co-containing structure, so that thedesired thickness of the Co-containing structure is obtained for thetarget lattice constant (e.g. as indicated in FIG. 11). In someembodiments, the Co-containing structure is in contact with theIr-containing structure. For example, the Ir-containing structure mayoverlie the Co-containing structure or the Co-containing structure maybe sandwiched between the Ir-containing structure and the first magneticlayer. In some embodiments, the Ir-containing structure and theCo-containing structure together form a templating structure having athickness in the range of at least ten Angstroms to not more than sixhundred Angstroms (e.g. at least 20 to not more than 500 Å in somecases), with an in-plane lattice constant in the range of 2.7 Angstromsto not more than 3.1 Angstroms (e.g. at least 2.82 Å to not more than3.03 Å). This templating structure may be advantageously annealed priorto depositing the first magnetic layer. In some embodiments, the annealtemperature is at least 200° C.

In the event that the structure is extended to include a tunnel barrier(see below in connection with FIGS. 17 and 18), the method includesforming a tunnel barrier over the first magnetic layer. In operation,current may passes through both the tunnel barrier and the firstmagnetic layer. An optional polarization enhancement layer between thefirst magnetic layer and the tunnel barrier may also be included. Asecond magnetic layer above (e.g., in contact with) the tunnel barriermay also be included. The tunnel barrier may be MgO orMg_(1-z)Al_(2+(2/3)z)O₄, wherein −0.5<z<0.5. As shown in the embodimentsof FIGS. 17 and 18, a capping layer may be deposited over (e.g., incontact with) the second magnetic layer. In one aspect of the method,the structure may be formed so that current can pass through the tunnelbarrier and both magnetic layers.

A structure including or consisting of a templating structure with aHeusler layer placed on a substrate with an optional seed layer can beused to fabricate racetrack memory devices. An embodiment of such astructure is depicted in FIG. 16. Magnetic domain walls may be movedalong such a racetrack. Data may be read out of (and stored in) theracetrack by interrogating (or changing) the orientation of the magneticmoment of the magnetic material between adjacent domain walls within theracetrack.

The structure described above with respect to FIG. 16 can also be usedas part of a MRAM memory device. Two possible configurations are shownin FIGS. 17 and 18, in which the switchable layers are different, withthe Heusler layer described herein being switchable in FIG. 17 but notin FIG. 18. As with MRAM elements generally, a tunnel barrier issituated between two magnetic electrodes, one of which has a fixedmagnetic moment and the other of which has a magnetic moment that isswitchable, thereby permitting the recording and erasing of data. Insome embodiments, the Heusler layer, which may be either ferro- orferri-magnetic, overlies a templating layer which in turn overlies asubstrate; the Heusler layer has its magnetic moment alignedperpendicular to the layer plane. An optional seed layer may beinterposed between the substrate and the templating layer. An optionalpolarization enhancement layer may be used to increase performance andmay include Fe, a CoFe alloy, and/or Co₂MnSi. The tunnel barrier may beMgO (001), although other (001)-oriented tunnel barriers may be used,such as CaO and LiF. In some embodiments, MgAl₂O₄ can be used as atunnel barrier whose lattice spacing can be tuned (engineered) bycontrolling the Mg—Al composition to result in better lattice matchingwith the Heusler compounds (e.g., the composition of this tunnel barriercan be represented as Mg_(1-z)Al_(2+(2/3)z)O₄, wherein −0.5<z<0.5). Themagnetic electrode overlying the tunnel barrier may comprise Fe, a CoFealloy, and/or a CoFeB alloy, for example. If the magnetic layer on topof the barrier has a fixed magnetic moment, its moment can be stabilizedby placing a synthetic antiferromagnet (SAF) in proximity with it. Thecapping layer may comprise Mo, W, Ta, Ru, or a combination thereof.Current may be induced by applying a voltage between the two magneticelectrodes, which are separated by the tunnel barrier.

IrAl Templating Layer as a SAF Spacer Layer

FIG. 2 shows that the use of an IrAl spacer layer between layers ofHeusler compounds can promote the formation of an SAF structure. TheIrAl alloy spacer layer forms a structure of the CsCl structure type (Irand Al form alternating layers) on top of the bottom Heusler layer (X₃Zin FIG. 2). This IrAl alloy spacer layer templates the top Heusler layer(X′₃Z′ in FIG. 2) and promotes anti-ferromagnetic coupling between twotetragonal Heusler layers. IrGa, an alloy which also has the CsClstructure, is expected to induce similar Heusler SAF structures, in viewof theoretical predictions. Moreover, substituting Ir—Ru for Ir withinIrAl (Ir_(x)Ru_(1-x) with x in the range 0.0001 to 0.9999) will alsoinduce anti-ferromagnetic coupling between two tetragonal Heuslercompound layers. Likewise, IrGe would be expected to work as atemplating layer for the top Heusler layer. Alternatively, an alloy oftwo or more of Al, Ga, and Ge could be used in combination with Ir orIr—Ru.

FIG. 19 includes a P-MOKE hysteresis loop obtained from a sample withtwo different layers of Heusler compounds separated by a non-magneticspacer layer of IrAl. The stack of this sample was MgO(001)/20 Å MgO/100Å CoAl/12 Å Mn₃Sn/t=11Å IrAl/20 Å Mn_(2.4)Sb/20 Å MgO/20 Å Ta (where “t”represents thickness). Three distinct hysteresis loops are observed, andthe sets of pairs of arrows overlaid in FIG. 19 indicate theorientations of the magnetization of the Mn₃Sn and Mn_(2.4)Sb layers. Athigh applied fields (e.g. greater than 1.5 kOe), the magnetizations ofthe two Heusler compounds are parallel to each other and align with theexternally applied field. At zero applied field, in the remanent state,the magnetizations of the two Heusler compounds are anti-parallel toeach other. Thus, the presence of the 11Å IrAl spacer layer separatingthe two Heusler compounds promotes the formation of a syntheticanti-ferromagnet (SAF). Moreover, the Heusler compounds, along withtheir corresponding spacer layer, were deposited at room temperature,with the resulting SAF structure needing no subsequent annealing.Furthermore, in the case of two layers of Heusler compounds havingmagnetic moments that are in-plane, the presence of an 11Å IrAl spacerlayer separating these two Heusler layers also leads to the formation ofa synthetic anti-ferromagnet (SAF). More explicitly, here the magneticmoments of the Heusler layers are substantially parallel to theinterfaces between the Heusler layers and the IrAl spacer layerseparating them. In some embodiments, the magnetic moments of the twoHeusler layers may be substantially anti-parallel to each other when theIrAl spacer layer has a thickness in the range of at least 3 to not morethan 11 Å. In some embodiments, the IrAl spacer has a thickness of atleast eight and not more than ten Angstroms. Moreover, the spacer layerproviding anti-ferromagnetic coupling between the two Heusler compoundscan be of the form D′Al (where D′ represents Ir or an IrRu alloy) orIrE′ (where E′ is selected from the group consisting of Al, Ga, and Ge,and combinations thereof) or D′E′ (where, for example, D′ is an IrRualloy and E′ is an AlGa alloy).

Although the thickness of each of the Heusler layers within the SAFstructure used herein was 1-2 nm, it is possible to form SAF structureswith other thicknesses (e.g. significantly thicker) of Heusler layers.The Heusler layers within the bilayer may have thicknesses of less than5 nm, or even less than 3 nm, or as little as the thickness of a singleunit cell (e.g., 0.7-0.8 nm). Though formation of the SAF isdemonstrated herein for two Heusler compounds, in general the Heuslercompounds can be selected from the group including or consisting ofMn_(3.1-x)Ge, Mn_(3.1-x)Sn, and Mn_(3.1-x)Sb, with x being in the rangefrom 0 to 1.1. Alternatively, the Heusler compounds may be a ternaryHeusler, such as Mn_(3.1-x)Co_(1.1-y)Sn, wherein x≤1.2 and y≤1.0. TheHeusler SAF structure can comprise a ternary Heusler compound as eitherthe first Heusler layer, the second Heusler layer, or both Heuslerlayers.

Mn_(2.3-2.4)Sb may be considered a Heusler or as part of the family ofL1₀ compounds. Hence the results discussed above indicate that the IrAltemplating spacer layer would also be effective in inducing SAF orderingbetween two L1₀ compounds (whose constituent elements include onetransition metal element and a main group element). Possible L1₀compounds include MnAl alloys, MnGa alloys, MnSn alloys, MnGe alloys,and FeAl alloys.

FIG. 20 summarizes the P-MOKE hysteresis loops measured from sampleshaving two layers of different Heusler compounds separated by anon-magnetic spacer layer of IrAl (of varying thickness, t). The stackof these samples was MgO(001)/20 Å MgO/100 Å CoAl/12 Å Mn₃Sn/t=7, 9, and11 Å IrAl/20 Å Mn_(2.4)Sb/20 Å MgO/20 Å Ta. For all these samples witht=7, 9, and 11 Å of IrAl, the coupling between the Heusler layers isanti-ferromagnetic.

FIG. 21 compares the P-MOKE hysteresis loops measured from samples withtwo Heusler compound layers separated by a non-magnetic spacer layer ofCoAl. The spacer layer thickness t is varied from 0 to 16 Å (t=0, 4, 6,7, 9, 10, 12, 14 and 16 Å). The stack of these samples was MgO(001)/20 ÅMgO/50 Å CoAl/12 Å Mn₃Ge/t CoAl/20 Å Mn_(2.3)Sb/20 Å MgO/20 Å Ta. Thehysteresis loops obtained for samples with a CoAl spacer layer show asingle square hysteresis loop at all CoAl thicknesses studied, which isdifferent from the hysteresis loops obtained for samples with an IrAlspacer layer. The Heusler compound layers separated by the CoAl spacerlayer are coupled ferromagnetically for all thicknesses, and there is noevidence that an SAF structure is formed.

A structure comprising a templating layer and a Heusler SAF, grown on asubstrate with an optional seed layer, can be used to fabricateracetrack memory devices (e.g. the devices depicted in FIGS. 22 and 23).Magnetic domain walls may be moved along such a racetrack. Data may beread out of (and stored in) the racetrack by interrogating (or changing)the orientation of the magnetic moment of the magnetic material betweenadjacent domain walls within the racetrack.

FIG. 22 shows a synthetic antiferromagnet that employs magnetic Heuslerlayers, such as those described herein. The top three layers of thestructure shown in FIG. 22 are now described in turn. The bottom-most ofthese three structures is a first magnetic layer that includes a Heuslercompound (and/or an L1₀ compound, such as one or more of MnGa, MnAl,FeAl, MnGe, MnSb, and MnSn).

Overlying the first magnetic layer is a first multi-layered structurethat is non-magnetic at room temperature; the first multi-layeredstructure (i) overlies the first magnetic layer and (ii) includesalternating layers of D′ and E′, in which E′ comprises a member selectedfrom a first group consisting of Al, Ga, Ge, and combinations thereof.The composition of the first multi-layered structure can be representedby D′_(i-y)E′_(y), with y being in the range from at least 0.4 to notmore than 0. (e.g. at least 0.47 to not more than 0.54), and theselected member of the first group representing at least 50 atomicpercent of E′. On the other hand, D′ comprises a member selected from asecond group consisting of Ir and an IrRu alloy, in which the selectedmember of the second group represents at least 50 atomic percent of D′.

Overlying the first multi-layered structure is a second magnetic layerthat includes a Heusler compound (and/or an L1₀ compound, such as thosedescribed above in connection with the first magnetic layer). The secondmagnetic layer is in contact with and overlies the first multi-layeredstructure. Together, the first magnetic layer, the first multi-layeredstructure, and the second magnetic layer (the top three layers shown inFIG. 22) form a synthetic antiferromagnet (SAF).

In some embodiments, a second multi-layered structure underlies and iscontact with the SAF (e.g. the templating layer of FIG. 22). This secondmulti-layered structure acts as a templating layer for the SAF. It isnon-magnetic at room temperature and includes alternating layers of Dand E, in which E comprises a member selected from a third groupconsisting of Al, Ga, Ge, and combinations thereof. The composition ofthe second multi-layered structure is represented by D_(1-x)E_(x), withx being in the range from 0.4 to not more than 0.6 (e.g. 0.47 to 0.54),and the selected member of the third group represents at least 50 atomicpercent of E (i.e. E includes at least fifty atomic percent of Al, Ga,Ge, or a combination thereof). D comprises a member selected from afourth group consisting of Ir, Co, Ru, and combinations thereof, whereinthe selected member of the fourth group represents at least 50 atomicpercent of D (i.e. D includes at least fifty atomic percent of Ir, Co,Ru, or a combination thereof). This second multi-layered structureunderlies and contacts the first magnetic layer.

In the device of FIG. 22, the magnetic moments of the first and secondmagnetic layers are substantially perpendicular to the interfacesbetween (i) the first multi-layered structure and (ii) the first andsecond magnetic layers, respectively. In FIG. 23, a similar device isshown in which the magnetic moments of the first and second magneticlayers are substantially parallel to the interfaces between (i) thefirst multi-layered structure and (ii) the first and second magneticlayers, respectively. The devices of FIGS. 22 and 23 are otherwiseidentical in some embodiments. Note that as with SAF structuresgenerally, the magnetic moments of the first and second magnetic layersare substantially anti-parallel to each other.

In some embodiments, the devices of FIGS. 22 and 23 have one or more ofthe following properties. The thickness of each of the first and secondmagnetic layers may be less than 5 nm or even 3 nm, whereas thethickness of the first multi-layered structure may be in the range of 3to 11 Å. In some embodiments, the first multi-layered structure has athickness of at least eight Angstroms and not more than ten Angstroms.The first and second magnetic layers include Heusler compounds(optionally doped with Co) independently selected from the groupconsisting of Mn_(3.1-x)Ge, Mn_(3.1-x)Sn, and Mn_(3.1-x)Sb (with x beingin the range from 0 to 1.1 in the case of Mn_(3.1-x)Sb, and with x beingin the range from 0 to 0.6 for Mn_(3.1-x)Ge and Mn_(3.1-x)Sn). In someembodiments, the first and/or the second magnetic layers may include aternary Heusler compound, such as Mn_(3.1-x)Co_(1.1-y)Sn, in which x≤1.2and y≤1.0. In some embodiments, the first and/or the second magneticlayers may include L1₀ compounds such as MnAl alloys, MnGa alloys, MnSnalloys, MnGe alloys, and FeAl alloys.

In some embodiments of the structures shown in FIGS. 22 and 23, at leastone of E and E′ is an AlGe alloy and/or an AlGa alloy. Alternatively, atleast one of E and E′ includes an alloy selected from the groupconsisting of AlSn, AlGe, AlGaGe, AlGaSn, AlGeSn, and AlGaGeSn. Also, aseed layer may be used advantageously over the substrate. The devices ofFIGS. 22 and 23 may be used as memory elements, for example, as part ofa racetrack memory device.

The structures described above in FIGS. 22 and 23 can also form part ofan MRAM element. Specifically, when additional components areintroduced, such as those shown in FIG. 24, an MRAM element may beformed, in which current passes through the tunnel barrier and adjoiningelements, in turn. As with MRAM memory elements generally, a tunnelbarrier (or other nonmagnetic layer) is situated between two magneticelectrodes, one of which has a fixed magnetic moment and the other ofwhich has a magnetic moment that is switchable, thereby permitting therecording and erasing of data. Unlike conventional MRAM elements,however, the magnetic layers of FIG. 24 having fixed magnetic moments(e.g. within the SAF pinning layer) each comprise a Heusler compoundlayer and are separated by a non-magnetic spacer. The Heusler layers,which may be either ferro- or ferri-magnetic, overlie a templating layerwhich in turn overlies a substrate; the Heusler layers have theirrespective magnetic moments oriented perpendicular to the layer plane(or in plane). In some embodiments, a Heusler based SAF structure may beused as a storage layer. An optional seed layer may be interposedbetween the substrate and the templating layer. An optional polarizationlayer may be used to increase performance, which may include Fe, a CoFealloy, and/or Co₂MnSi. The tunnel barrier may be MgO (001), althoughother (001)-oriented tunnel barriers may be used, such as CaO and LiF.Alternatively, MgAl₂O₄ can be used as a tunnel barrier; its latticespacing can be selected by controlling the Mg—Al composition to resultin better lattice matching with the Heusler compounds (e.g., thecomposition of this tunnel barrier can be represented asMg_(1-z)Al_(2+(2/3)z)O₄, wherein −0.5<z<0.5). The magnetic electrodeoverlying the tunnel barrier may be advantageously switchable and maycomprise Fe, a CoFe alloy, and/or a CoFeB alloy, for example. Thecapping layer may include Mo, W, Ta, Ru, or a combination thereof.Current may be induced by applying a voltage between the two magneticelectrodes, which are separated by the tunnel barrier.

The various layers described herein may be deposited through any one ormore of various methods, including magnetron sputtering,electrodeposition, ion beam sputtering, atomic layer deposition,chemical vapor deposition, and thermal evaporation.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is therefore indicated by theappended claims rather than the foregoing description. All changeswithin the meaning and range of equivalency of the claims are to beembraced within that scope.

TABLE 1 Target to Substrate Target Material Distance Ir-RBS (%) Al-RBS(%) IrAl 135 mm 52.5 47.5 IrAl 125 mm 49.9 50.1 IrAl 120 mm 49.5 50.5IrAl 113 mm 46.6 53.4

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

WHAT IS CLAIMED IS:

1. A device, comprising: a templating structure including D and E, aratio of D to E being represented by D_(1-x)E_(x), with x being at least0.4 and not more than 0.6, E including a main constituent, the mainconstituent including at least one of Al, Ga, and Ge, E including atleast fifty atomic percent of the main constituent, D including at leastone constituent that includes Ir, D including at least 50 atomic percentof the at least one constituent, the templating structure beingnonmagnetic at room temperature; and a magnetic layer on the templatingstructure, the magnetic layer including at least one of a Heuslercompound and an L1₀ compound, the magnetic layer being in contact withthe templating structure.
 2. The device of claim 1, wherein thetemplating structure includes alternating layers of D and E.
 3. Thedevice of claim 2, wherein x is at least 0.47 and not more than 0.54. 4.The device of claim 2, wherein the templating structure has a thicknessof at least thirty Angstroms and not more than six hundred Angstromssuch that the templating structure has a lattice constant of at least2.8 Angstroms and not more than 3.05 Angstroms.
 5. The device of claim2, wherein the magnetic layer has a thickness of not more than fivenanometers.
 6. The device of claim 5, wherein the magnetic layer has athickness of not more than one unit cell.
 7. The device of claim 2,wherein the magnetic layer includes at least one of Mn_(3.1-y)Ge,Mn_(3.1-y)Sn, Mn_(3.1-y)Sb, Mn_(3.1-s)Co_(1.1-t)Sn, a MnGa alloy, a MnAlalloy, an FeAl alloy, a MnGe alloy, a MnSb alloy, and a MnSn alloy, withy being at least 0 and not more than 1.1, and with s being greater thanzero and not more than 1.2 and t being greater than zero and not morethan 1.0.
 8. The device of claim 1, further comprising: an additionalmagnetic layer; and a tunneling barrier layer between the additionalmagnetic layer the magnetic layer.
 9. The device of claim 1, wherein themagnetic layer is magnetic as-deposited at room temperature.
 10. Adevice, comprising: a templating structure including D and E, a ratio ofD to E being represented by D_(1-x)E_(x), with x being at least 0.4 andnot more than 0.6, E including a main constituent, the main constituentincluding at least one of Al, Ga, and Ge, E including at least fiftyatomic percent of is the main constituent, D including at least oneconstituent that includes Ir, D including at least 50 atomic percent ofthe at least one constituent, the templating structure being nonmagneticat room temperature, the templating structure having a thickness of atleast thirty Angstroms and not more than six hundred Angstroms such thatthe templating structure has a lattice constant of at least 2.8Angstroms and not more than 3.05 Angstroms; and a magnetic layer on thetemplating structure, the magnetic layer including at least one of aHeusler compound and an L1₀ compound, the magnetic layer being incontact with the templating structure and being magnetic as-deposited atroom temperature.
 11. A method, comprising: providing a templatingstructure including D and E, a ratio of D to E being represented byD_(1-x)E_(x), with x being at least 0.4 and not more than 0.6, Eincluding a main constituent, the main constituent including at leastone of Al, Ga, and Ge, E including at least fifty atomic percent of themain constituent, D including at least one constituent that includes Ir,D including at least 50 atomic percent of the at least one constituent,the templating structure being nonmagnetic at room temperature; andproviding a magnetic layer on the templating structure, the magneticlayer including at least one of a Heusler compound and an L1₀ compound,the magnetic layer being in contact with the templating structure. 12.The method of claim 11, wherein providing the templating structureincludes: depositing alternating layers of D and E.
 13. The method ofclaim 12, wherein x is at least 0.47 and not more than 0.54.
 14. Themethod of claim 12, further comprising: selecting a target latticeconstant of the magnetic layer; and wherein the providing the templatingstructure further includes depositing the templating structure to athickness of at least thirty Angstroms and not more than six hundredAngstroms such that the templating structure has a lattice constant ofat is least 2.8 Angstroms and not more than 3.05 Angstroms, the latticeconstant corresponding to the target lattice constant.
 15. The method ofclaim 12, wherein the magnetic layer has a thickness of not more thanfive nanometers.
 16. The method of claim 15, wherein the magnetic layerhas a thickness of not more than one unit cell.
 17. The method of claim12, wherein the magnetic layer includes at least one of Mn_(3.1-y)Ge,Mn_(3.1-y)Sn, Mn_(3.1-y)Sb, Mn_(3.1-s)Co_(1.1-t)Sn, a MnGa alloy, a MnAlalloy, an FeAl alloy, a MnGe alloy, a MnSb alloy, and a MnSn alloy, withy being at least 0 and not more than 1.1, and with s being greater thanzero and not more than 1.2 and t being greater than zero and not morethan 1.0.
 18. The method of claim 11, further comprising: providing anadditional magnetic layer; and providing a tunneling barrier layerbetween the additional magnetic layer the magnetic layer.
 19. The methodof claim 11, wherein providing the magnetic layer further includes:depositing the magnetic layer at room temperature.
 20. The method ofclaim 11, wherein the providing the templating structure furtherincludes: annealing the templating structure at an anneal temperature ofat least two hundred degrees Celsius.